Optical fiber bending mechanisms

ABSTRACT

Fiber bending mechanisms vary beam characteristics by deflecting or bending one or more fibers, by urging portions of one or more fibers toward a fiber shaping surface having a selectable curvature, or by selecting a fiber length that is to be urged toward the fiber shaping surface. In some examples, a fiber is secured to a flexible plate to conform to a variable curvature of the flexible plate. In other examples, a variable length of a fiber is pulled or pushed toward a fiber shaping surface, and the length of the fiber or a curvature of the flexible plate provide modification of fiber beam characteristics.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/607,399, filed May 26, 2017, U.S. patent application Ser.No. 15/607,410, filed May 26, 2017, U.S. patent application Ser. No.15/607,411, filed May 26, 2017, and Patent Cooperation Treat ApplicationNo. PCT/US2017/034848, filed May 26, 2017, all of which claim thebenefit of U.S. Provisional Application No. 62/401,650, filed Sep. 29,2016. These applications are incorporated by reference herein in theirentireties.

FIELD

The disclosure pertains to beam shaping in optical fibers.

BACKGROUND

The use of high-power fiber-coupled lasers continues to gain popularityfor a variety of applications, such as materials processing, cutting,welding, and/or additive manufacturing. These lasers include, forexample, fiber lasers, disk lasers, diode lasers, diode-pumped solidstate lasers, and lamp-pumped solid state lasers. In these systems,optical power is delivered from the laser to a work piece via an opticalfiber.

Various fiber-coupled laser materials processing tasks require differentbeam characteristics (e.g., spatial profiles and/or divergenceprofiles). For example, cutting thick metal and welding generallyrequire a larger spot size than cutting thin metal. Ideally, the laserbeam properties would be adjustable to enable optimized processing forthese different tasks. Conventionally, users have two choices: (1)Employ a laser system with fixed beam characteristics that can be usedfor different tasks but is not optimal for most of them (i.e., acompromise between performance and flexibility); or (2) Purchase a lasersystem or accessories that offer variable beam characteristics but thatadd significant cost, size, weight, complexity, and perhaps performancedegradation (e.g., optical loss) or reliability degradation (e.g.,reduced robustness or up-time). Currently available laser systemscapable of varying beam characteristics require the use of free-spaceoptics or other complex and expensive add-on mechanisms (e.g., zoomlenses, mirrors, translatable or motorized lenses, combiners, etc.) inorder to vary beam characteristics. No solution exists that provides thedesired adjustability in beam characteristics that minimizes oreliminates reliance on the use of free-space optics or other extracomponents that add significant penalties in terms of cost, complexity,performance, and/or reliability. What is needed is an in-fiber apparatusfor providing varying beam characteristics that does not require orminimizes the use of free-space optics and that can avoid significantcost, complexity, performance tradeoffs, and/or reliability degradation.

SUMMARY

Apparatus comprise a first fiber situated to receive an input opticalbeam, the first fiber having a first refractive index profile. A fibershaping surface is situated so that a section of at least the firstfiber is urged to conform a fiber shaping surface. A bend controller issituated to select a length of the section of the first fiber urged toconform to the fiber shaping surface or to select a curvature of thefiber shaping surface to perturb the input optical beam and produce amodified optical beam. A second fiber is coupled to the first fiber andsituated to receive the modified optical beam, the second fiber having asecond refractive index profile selected to maintain at least one beamcharacteristic of the modified optical beam. In some examples, the fibershaping surface is a major surface of a flexible plate, and the flexibleplate includes an ionic-polymer composite. In other alternatives, apiezo-bending actuator is used that can include one or morepiezoelectric plates bonded together. Typically, a first electrode and asecond electrode are situated so that at least a portion of the ionicpolymer is situated between the first electrode and the secondelectrode. In some examples, the first electrode and the secondelectrode are conductive layers that substantially cover the first majorsurface and the second major surface, and the bend controller is anelectrical voltage source. In further examples, a second set ofelectrodes is situated about the ionic polymer and a sensor is coupledto the second set of electrodes to detect deformation of the flexibleplate. The bend controller is coupled to the sensor and establishes avoltage applied to the ionic polymer based on a voltage detected by thesecond set of electrodes.

According to some examples, the first fiber is situated to as to extendalong a direction of the curvature of the fiber shaping surface. Inother examples, the first fiber comprises one or more elongated loopsand the section of the fiber conforming to the fiber shaping surfaceincludes elongated portions of the loops situated to extend in thedirection of the curvature of the fiber shaping surface. In otherembodiments, a displacement member is coupled to the flexible plate tovary the curvature of the fiber shaping surface by pushing against theflexible plate or pulling the flexible plate. In typical examples, theflexible plate is secured at two locations and the displacement memberis coupled to the flexible plate between the two locations. Inrepresentative embodiments, the flexible plate is secured at respectiveends along a direction of the curvature of the fiber shaping surface.According to some examples, the fiber shaping surface has a fixedcurvature, and is a surface of a ring, a surface of a section of a ring,or an outer surface of a cylinder such as a right circular cylinder.

In some examples, the bend controller is situated to vary the length ofthe section of the first fiber that conforms to the fiber shapingsurface. In additional examples, a guide is slidably secured withrespect to the flexible surface and situated to engage the fiber so thatthe length of the section of the first fiber that is urged to conform tothe fiber shaping surface is variable in response to movement of theguide along the fiber shaping surface. In some examples, the guideincludes a groove that engages the first fiber. In still furtherembodiments, a connecting member is rotatably secured at an axis ofrotation and secured to the guide so that rotation of the guide aboutthe axis urges the guide along the fiber shaping surface. According toadditional examples, the fiber shaping surface has a compound curvaturethat includes a plurality of circular curvatures, and the axis ofrotation corresponds to a center of curvature of one of the plurality ofthe circular curvatures.

According to some examples, the fiber shaping surface is defined by aportion of a mandrel surface and the bend controller comprises a jawsituated to urge the first length of fiber toward the portion of themandrel surface and the first fiber forms at least a portion of a loopsituated about the mandrel. In some cases, the bend controller includesa stage situated to urge the mandrel towards the first length of fiber.In additional examples, the first fiber and the second fiber form atleast the portion of the loop. A splice couples the first fiber and thesecond fiber and the jaw is situated to urge the first length of fiber,a portion of the second fiber, and the splice toward the portion of themandrel surface. In still further examples, the jaw comprises a firstjaw and a second jaw oppositely situated with respect to a displacementaxis of the stage. The first jaw and the second jaw are coupled to afirst elastic member and a second elastic member each situated to urge arespective jaw surface toward the mandrel surface. In other examples,the bend controller is configured to urge the mandrel toward the firstjaw surface and the second jaw surface so as to select the section ofthe first fiber that is urged to conform to the fiber shaping surface, asection of the second fiber that is urged to conform to the fibershaping surface, and a curvature of at least a portion of the loop thatdoes not contact either the fiber bending surface, the first, jaw, orthe second jaw.

In some examples, fiber sections are secured at one or two end points,or formed in curved, looped, or straight sections, and one or moresurfaces such as surfaces of pins, rods, or spheres contact the fibersections, and a fiber is bent in response. In some examples, the fibersections are urged toward such a surface, or the surface is urged towardthe fiber section, or both are movable toward each other.

The foregoing and other objects, features, and advantages of thedisclosed technology will become more apparent from the followingdetailed description, which proceeds with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, wherein like reference numerals representlike elements, are incorporated in and constitute a part of thisspecification and, together with the description, explain the advantagesand principles of the presently disclosed technology. In the drawings,

FIG. 1 illustrates an example fiber structure for providing a laser beamhaving variable beam characteristics;

FIG. 2 depicts a cross-sectional view of an example fiber structure fordelivering a beam with variable beam characteristics;

FIG. 3 illustrates an example method of perturbing a fiber structure forproviding a beam having variable beam characteristics;

FIG. 4 is a graph illustrating the calculated spatial profile of thelowest-order mode (LP₀₁) for a first length of a fiber for differentfiber bend radii;

FIG. 5 illustrates an example of a two-dimensional intensitydistribution at a junction when a fiber for varying beam characteristicsis nearly straight;

FIG. 6 illustrates an example of a two-dimensional intensitydistribution at a junction when a fiber for varying beam characteristicsis bent with a radius chosen to preferentially excite a particularconfinement region of a second length of fiber;

FIGS. 7-10 depict experimental results to illustrate further outputbeams for various bend radii of a fiber for varying beam characteristicsshown in FIG. 2;

FIGS. 11-16 illustrate cross-sectional views of example first lengths offiber for enabling adjustment of beam characteristics in a fiberassembly;

FIGS. 17-19 illustrate cross-sectional views of example second lengthsof fiber (“confinement fibers”) for confining adjusted beamcharacteristics in a fiber assembly;

FIGS. 20 and 21 illustrate cross-sectional views of example secondlengths of fiber for changing a divergence angle of and confining anadjusted beam in a fiber assembly configured to provide variable beamcharacteristics;

FIG. 22A illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and process head;

FIG. 22B illustrates an example a laser system including a fiberassembly configured to provide variable beam characteristics disposedbetween a feeding fiber and process head;

FIG. 23 illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and multiple process fibers;

FIG. 24 illustrates examples of various perturbation assemblies forproviding variable beam characteristics according to various examplesprovided herein;

FIG. 25 illustrates an example process for adjusting and maintainingmodified characteristics of an optical beam; and

FIGS. 26-28 are cross-sectional views illustrating example secondlengths of fiber (“confinement fibers”) for confining adjusted beamcharacteristics in a fiber assembly.

FIGS. 29A-29C illustrate a variable beam characteristics (VBC) apparatusthat includes an optical fiber bending mechanism having rollers situatedto push a selectable length of an optical fiber against a mandrel havinga circular cross-section.

FIG. 30 illustrates a fiber bending mechanism that can accommodatemultiple fiber loops.

FIG. 31 illustrates VBC apparatus that includes rollers situated to pusha selectable length of an optical fiber against a mandrel having anelliptical cross-section.

FIG. 32 illustrates a representative fiber shaping surface.

FIGS. 33A-33B illustrate another beam perturbation device that includesa fiber bending mechanism.

FIG. 34 illustrates another beam perturbation device that includes afiber bending mechanism having a fiber shaping surface on a section of adisc.

FIG. 35 illustrates another beam perturbation device that includes afiber bending mechanism having a fiber shaping surface on a portion of aring.

FIG. 36 illustrates a VBC apparatus that includes a flexure to which anoptical fiber is secured.

FIGS. 37A-37B illustrates a fiber bending mechanism that varies a lengthof fiber that is bent.

FIGS. 38A-38B illustrate a VBC apparatus that includes optical fiberbending mechanism that urges a selected length of an optical fiber so asto contact oppositely situated jaws.

FIGS. 39A-39D illustrate operation of the optical fiber bendingmechanism of FIGS. 38A-38B.

FIG. 40 illustrates another representative VBC apparatus that includeoppositely situated sets of cylinders that can contact a fiber.

FIG. 41 illustrates a representative fiber shaping surface formed with aplurality of oppositely situated cylinders.

FIG. 42 illustrates another VBC apparatus that includes a flexure towhich an optical fiber is secured.

FIGS. 43A-43B illustrate a spool that permits bending of selectablelengths of fiber.

FIGS. 44A-44B illustrate a VBC device that includes an ionic polymercomposite (IPC).

FIG. 45 illustrates illustrate another VBC device that includes an IPC.

FIG. 46 illustrates a representative VBC system.

FIGS. 47A-47C illustrate additional representative VBC apparatus.

DETAILED DESCRIPTION

As used herein throughout this disclosure and in the claims, thesingular forms “a,” “an,” and “the” include the plural forms unless thecontext clearly dictates otherwise. Additionally, the term “includes”means “comprises.” Further, the term “coupled” does not exclude thepresence of intermediate elements between the coupled items. Also, theterms “modify” and “adjust” are used interchangeably to mean “alter.”

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some examples, values, procedures, or apparatus are referred to as“lowest”, “best”, “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyused functional alternatives can be made, and such selections need notbe better, smaller, or otherwise preferable to other selections.Examples are described with reference to directions indicated as“above,” “below,” “upper,” “lower,” and the like. These terms are usedfor convenient description, but do not imply any particular spatialorientation.

Definitions

Definitions of words and terms as used herein:

-   1. The term “beam characteristics” refers to one or more of the    following terms used to describe an optical beam. In general, the    beam characteristics of most interest depend on the specifics of the    application or optical system.-   2. The term “beam diameter” is defined as the distance across the    center of the beam along an axis for which the irradiance    (intensity) equals 1/e² of the maximum irradiance. While examples    disclosed herein generally use beams that propagate in azimuthally    symmetric modes, elliptical or other beam shapes can be used, and    beam diameter can be different along different axes. Circular beams    are characterized by a single beam diameter. Other beam shapes can    have different beam diameters along different axes.-   3. The term “spot size” is the radial distance (radius) from the    center point of maximum irradiance to the 1/e² point.-   4. The term “beam divergence distribution” is the power vs the full    cone angle. This quantity is sometimes called the “angular    distribution” or “NA distribution.”-   5. The term “beam parameter product” (BPP) of a laser beam is    defined as the product of the beam radius (measured at the beam    waist) and the beam divergence half-angle (measured in the far    field). The units of BPP are typically mm-mrad.-   6. A “confinement fiber” is defined to be a fiber that possesses one    or more confinement regions, wherein a confinement region comprises    a higher-index region (core region) surrounded by a lower-index    region (cladding region). The RIP of a confinement fiber may include    one or more higher-index regions (core regions) surrounded by    lower-index regions (cladding regions), wherein light is guided in    the higher-index regions. Each confinement region and each cladding    region can have any RIP, including but not limited to step-index and    graded-index. The confinement regions may or may not be concentric    and may be a variety of shapes such as circular, annular, polygonal,    arcuate, elliptical, or irregular, or the like or any combination    thereof. The confinement regions in a particular confinement fiber    may all have the same shape or may be different shapes. Moreover,    confinement regions may be co-axial or may have offset axes with    respect to one another. Confinement regions may be of uniform    thickness about a central axis in the longitudinal direction, or the    thicknesses may vary about the central axis in the longitudinal    direction.-   7. The term “intensity distribution” refers to optical intensity as    a function of position along a line (1D profile) or on a plane (2D    profile). The line or plane is usually taken perpendicular to the    propagation direction of the light. It is a quantitative property.-   8. “Luminance” is a photometric measure of the luminous intensity    per unit area of light travelling in a given direction.-   9. “M² factor” (also called “beam quality factor” or “beam    propagation factor”) is a dimensionless parameter for quantifying    the beam quality of laser beams, with M²=1 being a    diffraction-limited beam, and larger M2 values corresponding to    lower beam quality. M² is equal to the BPP divided by λ/π, where λ    is the wavelength of the beam in microns (if BPP is expressed in    units of mm-mrad).-   10. The term “numerical aperture” or “NA” of an optical system is a    dimensionless number that characterizes the range of angles over    which the system can accept or emit light.-   11. The term “optical intensity” is not an official (SI) unit, but    is used to denote incident power per unit area on a surface or    passing through a plane.-   12. The term “power density” refers to optical power per unit area,    although this is also referred to as “optical intensity.”-   13. The term “radial beam position” refers to the position of a beam    in a fiber measured with respect to the center of the fiber core in    a direction perpendicular to the fiber axis.-   14. “Radiance” is the radiation emitted per unit solid angle in a    given direction by a unit area of an optical source (e.g., a laser).    Radiance may be altered by changing the beam intensity distribution    and/or beam divergence profile or distribution. The ability to vary    the radiance profile of a laser beam implies the ability to vary the    BPP.-   15. The term “refractive-index profile” or “RIP” refers to the    refractive index as a function of position along a line (1D) or in a    plane (2D) perpendicular to the fiber axis. Many fibers are    azimuthally symmetric, in which case the 1D RIP is identical for any    azimuthal angle.-   16. A “step-index fiber” has a RIP that is flat (refractive index    independent of position) within the fiber core.-   17. A “graded-index fiber” has a RIP in which the refractive index    decreases with increasing radial position (i.e., with increasing    distance from the center of the fiber core).-   18. A “parabolic-index fiber” is a specific case of a graded-index    fiber in which the refractive index decreases quadratically with    increasing distance from the center of the fiber core.-   19. “Free space propagation” and “unguided propagation” are used to    refer to optical beams that propagate without being constrained to    one or more waveguides (such as optical fibers) over optical    distances that are typically 5, 10, 20, 100 times or more than a    beam Rayleigh range. Such propagation can be in optical media such    as glass, fused silica, semiconductors, air, crystalline materials,    or vacuum.-   20. “Collimated beams” are generally produced by situating a lens or    other focusing element such as a curved mirror, a Fresnel lens, or a    holographic optical element such that an apparent distance from a    location at which a beam has, would have, or appears to have a    planar wavefront (such as at a focus of a Gaussian beam or at an    output of an optical fiber) that is less than 10%, 5%, 2%, 1%, 0.5%,    0,1% of a focal length f from a focal point of a focal length f.

Fiber for Varying Beam Characteristics

Disclosed herein are methods, systems, and apparatus configured toprovide a fiber operable to provide a laser beam having variable beamcharacteristics (VBC) that may reduce cost, complexity, optical loss, orother drawbacks of the conventional methods described above. This VBCfiber is configured to vary a wide variety of optical beamcharacteristics. Such beam characteristics can be controlled using theVBC fiber thus allowing users to tune various beam characteristics tosuit the particular requirements of an extensive variety of laserprocessing applications. For example, a VBC fiber may be used to tune:beam diameter, beam divergence distribution, BPP, intensitydistribution, M² factor, NA, optical intensity, power density, radialbeam position, radiance, spot size, or the like, or any combinationthereof.

In general, the disclosed technology entails coupling a laser beam intoa fiber in which the characteristics of the laser beam in the fiber canbe adjusted by perturbing the laser beam and/or perturbing a firstlength of fiber by any of a variety of methods (e.g., bending the fiberor introducing one or more other perturbations) and fully or partiallymaintaining adjusted beam characteristics in a second length of fiber.The second length of fiber is specially configured to maintain and/orfurther modify the adjusted beam characteristics. In some cases, thesecond length of fiber preserves the adjusted beam characteristicsthrough delivery of the laser beam to its ultimate use (e.g., materialsprocessing). The first and second lengths of fiber may comprise the sameor different fibers.

The disclosed technology is compatible with fiber lasers andfiber-coupled lasers. Fiber-coupled lasers typically deliver an outputvia a delivery fiber having a step-index refractive index profile (RIP),i.e., a flat or constant refractive index within the fiber core. Inreality, the RIP of the delivery fiber may not be perfectly flat,depending on the design of the fiber. Important parameters are the fibercore diameter (d_(core)) and NA. The core diameter is typically in therange of 10-1000 micron (although other values are possible), and the NAis typically in the range of 0.06-0.22 (although other values arepossible). A delivery fiber from the laser may be routed directly to theprocess head or work piece, or it may be routed to a fiber-to-fibercoupler (FFC) or fiber-to-fiber switch (FFS), which couples the lightfrom the delivery fiber into a process fiber that transmits the beam tothe process head or the work piece.

Most materials processing tools, especially those at high power (>1 kW),employ multimode (MM) fiber, but some employ single-mode (SM) fiber,which is at the lower end of the d_(core) and NA ranges. The beamcharacteristics from a SM fiber are uniquely determined by the fiberparameters. The beam characteristics from a MM fiber, however, can vary(unit-to-unit and/or as a function of laser power and time), dependingon the beam characteristics from the laser source(s) coupled into thefiber, the launching or splicing conditions into the fiber, the fiberRIP, and the static and dynamic geometry of the fiber (bending, coiling,motion, micro-bending, etc.). For both SM and MM delivery fibers, thebeam characteristics may not be optimum for a given materials processingtask, and it is unlikely to be optimum for a range of tasks, motivatingthe desire to be able to systematically vary the beam characteristics inorder to customize or optimize them for a particular processing task.

In one example, the VBC fiber may have a first length and a secondlength and may be configured to be interposed as an in-fiber devicebetween the delivery fiber and the process head to provide the desiredadjustability of the beam characteristics. To enable adjustment of thebeam, a perturbation device and/or assembly is disposed in closeproximity to and/or coupled with the VBC fiber and is responsible forperturbing the beam in a first length such that the beam'scharacteristics are altered in the first length of fiber, and thealtered characteristics are preserved or further altered as the beampropagates in the second length of fiber. The perturbed beam is launchedinto a second length of the VBC fiber configured to conserve adjustedbeam characteristics. The first and second lengths of fiber may be thesame or different fibers and/or the second length of fiber may comprisea confinement fiber. The beam characteristics that are conserved by thesecond length of VBC fiber may include any of: beam diameter, beamdivergence distribution, BPP, intensity distribution, luminance, M²factor, NA, optical intensity, power density, radial beam position,radiance, spot size, or the like, or any combination thereof.

In some disclosed embodiments, a fiber is referred to a being urged toconform to a surface. Unless otherwise indicated, such a fiber need notcontact such a surface nor acquire a curvature corresponding to thesurface.

FIG. 1 illustrates an example VBC fiber 100 for providing a laser beamhaving variable beam characteristics without requiring the use offree-space optics to change the beam characteristics. VBC fiber 100comprises a first length of fiber 104 and a second length of fiber 108.First length of fiber 104 and second length of fiber 108 may be the sameor different fibers and may have the same or different RIPs. The firstlength of fiber 104 and the second length of fiber 108 may be joinedtogether by a splice. First length of fiber 104 and second length offiber 108 may be coupled in other ways, may be spaced apart, or may beconnected via an interposing component such as another length of fiber,free-space optics, glue, index-matching material, or the like or anycombination thereof.

A perturbation device 110 is disposed proximal to and/or envelopsperturbation region 106. Perturbation device 110 may be a device,assembly, in-fiber structure, and/or other feature. Perturbation device110 at least perturbs optical beam 102 in first length of fiber 104 orsecond length of fiber 108 or a combination thereof in order to adjustone or more beam characteristics of optical beam 102. Adjustment of beam102 responsive to perturbation by perturbation device 110 may occur infirst length of fiber 104 or second length of fiber 108 or a combinationthereof. Perturbation region 106 may extend over various widths and mayor may not extend into a portion of second length of fiber 108. As beam102 propagates in VBC fiber 100, perturbation device 110 may physicallyact on VBC fiber 100 to perturb the fiber and adjust the characteristicsof beam 102. Alternatively, perturbation device 110 may act directly onbeam 102 to alter its beam characteristics. Subsequent to beingadjusted, perturbed beam 112 has different beam characteristics thanbeam 102, which will be fully or partially conserved in second length offiber 108. In another example, perturbation device 110 need not bedisposed near a splice. Moreover, a splice may not be needed at all, forexample VBC fiber 100 may be a single fiber, first length of fiber andsecond length of fiber could be spaced apart, or secured with a smallgap (air-spaced or filled with an optical material, such as opticalcement or an index-matching material).

Perturbed beam 112 is launched into second length of fiber 108, whereperturbed beam 112 characteristics are largely maintained or continue toevolve as perturbed beam 112 propagates yielding the adjusted beamcharacteristics at the output of second length of fiber 108. In oneexample, the new beam characteristics may include an adjusted intensitydistribution. In an example, an altered beam intensity distribution willbe conserved in various structurally bounded confinement regions ofsecond length of fiber 108. Thus, the beam intensity distribution may betuned to a desired beam intensity distribution optimized for aparticular laser processing task. In general, the intensity distributionof perturbed beam 112 will evolve as it propagates in the second lengthof fiber 108 to fill the confinement region(s) into which perturbed beam112 is launched responsive to conditions in first length of fiber 104and perturbation caused by perturbation device 110. In addition, theangular distribution may evolve as the beam propagates in the secondfiber, depending on launch conditions and fiber characteristics. Ingeneral, fibers largely preserve the input divergence distribution, butthe distribution can be broadened if the input divergence distributionis narrow and/or if the fiber has irregularities or deliberate featuresthat perturb the divergence distribution. The various confinementregions, perturbations, and fiber features of second length of fiber 108are described in greater detail below. Beams 102 and 112 are conceptualabstractions intended to illustrate how a beam may propagate through aVBC fiber 100 for providing variable beam characteristics and are notintended to closely model the behavior of a particular optical beam.

VBC fiber 100 may be manufactured by a variety of methods including PCVD(Plasma Chemical Vapor Deposition), OVD (Outside Vapor Deposition), VAD(Vapor Axial Deposition), MOCVD (Metal-Organic Chemical VaporDeposition.) and/or DND (Direct Nanoparticle Deposition). VBC fiber 100may comprise a variety of materials. For example, VBC fiber 100 maycomprise SiO₂, SiO₂ doped with GeO₂, germanosilicate, phosphoruspentoxide, phosphosilicate, Al₂O₃, aluminosilicate, or the like or anycombinations thereof. Confinement regions may be bounded by claddingdoped with fluorine, boron, or the like or any combinations thereof.Other dopants may be added to active fibers, including rare-earth ionssuch as Er³+ (erbium), Yb³+ (ytterbium), Nd³+ (neodymium), Tm³+(thulium), Ho³+ (holmium), or the like or any combination thereof.Confinement regions may be bounded by cladding having a lower index thanthe confinement region with fluorine or boron doping. Alternatively, VBCfiber 100 may comprise photonic crystal fibers or micro-structuredfibers.

VBC fiber 100 is suitable for use in any of a variety of fiber, fiberoptic, or fiber laser devices, including continuous wave and pulsedfiber lasers, disk lasers, solid state lasers, or diode lasers (pulserate unlimited except by physical constraints). Furthermore,implementations in a planar waveguide or other types of waveguides andnot just fibers are within the scope of the claimed technology.

FIG. 2 depicts a cross-sectional view of an example VBC fiber 200 foradjusting beam characteristics of an optical beam. In an example, VBCfiber 200 may be a process fiber because it may deliver the beam to aprocess head for material processing. VBC fiber 200 comprises a firstlength of fiber 204 spliced at junction 206 to a second length of fiber208. A perturbation assembly 210 is disposed proximal to junction 206.Perturbation assembly 210 may be any of a variety of devices configuredto enable adjustment of the beam characteristics of an optical beam 202propagating in VBC fiber 200. In an example, perturbation assembly 210may be a mandrel and/or another device that may provide means of varyingthe bend radius and/or bend length of VBC fiber 200 near the splice.Other examples of perturbation devices are discussed below with respectto FIG. 24.

In an example, first length of fiber 204 has a parabolic-index RIP 212as indicated by the left RIP graph. Most of the intensity distributionof beam 202 is concentrated in the center of fiber 204 when fiber 204 isstraight or nearly straight. Second length of fiber 208 is a confinementfiber having RIP 214 as shown in the right RIP graph. Second length offiber 208 includes confinement regions 216, 218 and 220. Confinementregion 216 is a central core surrounded by two annular (or ring-shaped)confinement regions 218 and 220. Layers 222 and 224 are structuralbarriers of lower index material between confinement regions (216, 218and 220), commonly referred to as “cladding” regions. In one example,layers 222 and 224 may comprise rings of fluorosilicate; in someembodiments, the fluorosilicate cladding layers are relatively thin.Other materials may be used as well and claimed subject matter is notlimited in this regard.

In an example, as beam 202 propagates along VBC fiber 200, perturbationassembly 210 may physically act on fiber 208 and/or beam 202 to adjustits beam characteristics and generate adjusted beam 226. In the currentexample, the intensity distribution of beam 202 is modified byperturbation assembly 210. Subsequent to adjustment of beam 202 theintensity distribution of adjusted beam 226 may be concentrated in outerconfinement regions 218 and 220 with relatively little intensity in thecentral confinement region 216. Because each of confinement regions 216,218, and/or 220 is isolated by the thin layers of lower index materialin barrier layers 222 and 224, second length of fiber 208 cansubstantially maintain the adjusted intensity distribution of adjustedbeam 226. The beam will typically become distributed azimuthally withina given confinement region but will not transition (significantly)between the confinement regions as it propagates along the second lengthof fiber 208.

Thus, the adjusted beam characteristics of adjusted beam 226 are largelyconserved within the isolated confinement regions 216, 218, and/or 220.In some cases, it be may desirable to have the beam 226 power dividedamong the confinement regions 216, 218, and/or 220 rather thanconcentrated in a single region, and this condition may be achieved bygenerating an appropriately adjusted beam 226.

In one example, core confinement region 216 and annular confinementregions 218 and 220 may be composed of fused silica glass, and cladding222 and 224 defining the confinement regions may be composed offluorosilicate glass. Other materials may be used to form the variousconfinement regions (216, 218 and 220), including germanosilicate,phospho silicate, aluminosilicate, or the like, or a combination thereofand claimed subject matter is not so limited. Other materials may beused to form the barrier rings (222 and 224), including fused silica,borosilicate, or the like or a combination thereof, and claimed subjectmatter is not so limited. In other embodiments, the optical fibers orwaveguides include or are composed of various polymers or plastics orcrystalline materials. Generally, the core confinement regions haverefractive indices that are greater than the refractive indices ofadjacent barrier/cladding regions.

In some examples, it may be desirable to increase a number ofconfinement regions in a second length of fiber to increase granularityof beam control over beam displacements for fine-tuning a beam profile.For example, confinement regions may be configured to provide stepwisebeam displacement.

FIG. 3 illustrates an example method of perturbing fiber 200 forproviding variable beam characteristics of an optical beam. Changing thebend radius of a fiber may change the radial beam position, divergenceangle, and/or radiance profile of a beam within the fiber. The bendradius of VBC fiber 200 can be decreased from a first bend radius R₁ toa second bend radius R₂ about splice junction 206 by using a steppedmandrel or cone as the perturbation assembly 210. Additionally oralternatively, the engagement length on the mandrel(s) or cone can bevaried. Rollers 250 may be employed to engage VBC fiber 200 acrossperturbation assembly 210. In an example, an amount of engagement ofrollers 250 with fiber 200 has been shown to shift the distribution ofthe intensity profile to the outer confinement regions 218 and 220 offiber 200 with a fixed mandrel radius. There are a variety of othermethods for varying the bend radius of fiber 200, such as using aclamping assembly, flexible tubing, or the like, or a combinationthereof, and claimed subject matter is not limited in this regard. Inanother example, for a particular bend radius the length over which VBCfiber 200 is bent can also vary beam characteristics in a controlled andreproducible way. In examples, changing the bend radius and/or lengthover which the fiber is bent at a particular bend radius also modifiesthe intensity distribution of the beam such that one or more modes maybe shifted radially away from the center of a fiber core.

Maintaining the bend radius of the fibers across junction 206 ensuresthat the adjusted beam characteristics such as radial beam position andradiance profile of optical beam 202 will not return to beam 202′sunperturbed state before being launched into second length of fiber 208.Moreover, the adjusted radial beam characteristics, including position,divergence angle, and/or intensity distribution, of adjusted beam 226can be varied based on an extent of decrease in the bend radius and/orthe extent of the bent length of VBC fiber 200. Thus, specific beamcharacteristics may be obtained using this method.

In the current example, first length of fiber 204 having first RIP 212is spliced at junction 206 to a second length of fiber 208 having asecond RIP 214. However, it is possible to use a single fiber having asingle RIP formed to enable perturbation (e.g., by micro-bending) of thebeam characteristics of beam 202 and also to enable conservation of theadjusted beam. Such a RIP may be similar to the RIPs shown in fibersillustrated in FIGS. 17, 18, and/or 19.

FIGS. 7-10 provide experimental results for VBC fiber 200 (shown inFIGS. 2 and 3) and illustrate further a beam response to perturbation ofVBC fiber 200 when a perturbation assembly 210 acts on VBC fiber 200 tobend the fiber. FIGS. 4 6 are simulations and FIGS. 7-10 areexperimental results wherein a beam from a SM 1050 nm source waslaunched into an input fiber (not shown) with a 40 micron core diameter.The input fiber was spliced to first length of fiber 204.

FIG. 4 is an example graph 400 illustrating the calculated profile ofthe lowest-order mode (LP₀₁) for a first length of fiber 204 fordifferent fiber bend radii 402, wherein a perturbation assembly 210involves bending VBC fiber 200. As the fiber bend radius is decreased,an optical beam propagating in VBC fiber 200 is adjusted such that themode shifts radially away from the center 404 of a VBC fiber 200 core(r=0 micron) toward the core/cladding interface (located at r=100 micronin this example). Higher-order modes (LP_(In)) also shift with bending.Thus, a straight or nearly straight fiber (very large bend radius),curve 406 for LP₀₁ is centered at or near the center of VBC fiber 200.At a bend radius of about 6 cm, curve 408 for LP₀₁ is shifted to aradial position of about 40 μm from the center 406 of VBC fiber 200. Ata bend radius of about 5 cm, curve 410 for LP₀₁ is shifted to a radialposition about 50 μm from the center 406 of VBC fiber 200. At a bendradius of about 4 cm, curve 412 for LP₀₁ is shifted to a radial positionabout 60 μm from the center 406 of VBC fiber 200. At a bend radius ofabout 3 cm, curve 414 for LP₀₁ is shifted to a radial position about 80μm from the center 406 of VBC fiber 200. At a bend radius of about 2.5cm, a curve 416 for LP₀₁ is shifted to a radial position about 85 μmfrom the center 406 of VBC fiber 200. Note that the shape of the moderemains relatively constant (until it approaches the edge of the core),which is a specific property of a parabolic RIP. Although, this propertymay be desirable in some situations, it is not required for the VBCfunctionality, and other RIPs may be employed.

In an example, if VBC fiber 200 is straightened, LP₀₁ mode will shiftback toward the center of the fiber. Thus, the purpose of second lengthof fiber 208 is to “trap” or confine the adjusted intensity distributionof the beam in a confinement region that is displaced from the center ofthe VBC fiber 200. The splice between fibers 204 and 208 is included inthe bent region, thus the shifted mode profile will be preferentiallylaunched into one of the ring-shaped confinement regions 218 and 220 orbe distributed among the confinement regions. FIGS. 5 and 6 illustratethis effect.

FIG. 5 illustrates an example two-dimensional intensity distribution atjunction 206 within second length of fiber 208 when VBC fiber 200 isnearly straight. A significant portion of LP₀₁ and LP_(In) are withinconfinement region 216 of fiber 208. FIG. 6 illustrates thetwo-dimensional intensity distribution at junction 206 within secondlength of fiber 208 when VBC fiber 200 is bent with a radius chosen topreferentially excite confinement region 220 (the outermost confinementregion) of second length of fiber 208. A significant portion of LP₀₁ andLP_(In) are within confinement region 220 of fiber 208.

In an example, second length of fiber 208 confinement region 216 has a100 micron diameter, confinement region 218 is between 120 micron and200 micron in diameter, and confinement region 220 is between 220 micronand 300 micron diameter. Confinement regions 216, 218, and 220 areseparated by 10 μm thick rings of fluorosilicate, providing an NA of0.22 for the confinement regions. Other inner and outer diameters forthe confinement regions, thicknesses of the rings separating theconfinement regions, NA values for the confinement regions, and numbersof confinement regions may be employed.

Referring again to FIG. 5, with the noted parameters, when VBC fiber 200is straight about 90% of the power is contained within the centralconfinement region 216, and about 100% of the power is contained withinconfinement regions 216 and 218. Referring now to FIG. 6, when fiber 200is bent to preferentially excite second ring confinement region 220,nearly 75% of the power is contained within confinement region 220, andmore than 95% of the power is contained within confinement regions 218and 220. These calculations include LP₀₁ and two higher-order modes,which is typical in some 2-4 kW fiber lasers.

It is clear from FIGS. 5 and 6 that in the case where a perturbationassembly 210 acts on VBC fiber 200 to bend the fiber, the bend radiusdetermines the spatial overlap of the modal intensity distribution ofthe first length of fiber 204 with the different guiding confinementregions (216, 218, and 220) of the second length of fiber 208. Changingthe bend radius can thus change the intensity distribution at the outputof the second length of fiber 208, thereby changing the diameter or spotsize of the beam, and thus also changing its radiance and BPP value.This adjustment of the spot size may be accomplished in an all-fiberstructure, involving no free-space optics and consequently may reduce oreliminate the disadvantages of free-space optics discussed above. Suchadjustments can also be made with other perturbation assemblies thatalter bend radius, bend length, fiber tension, temperature, or otherperturbations discussed below.

In a typical materials processing system (e.g., a cutting or weldingtool), the output of the process fiber is imaged at or near the workpiece by the process head. Varying the intensity distribution as shownin FIGS. 5 and 6 thus enables variation of the beam profile at the workpiece in order to tune and/or optimize the process, as desired. SpecificRIPs for the two fibers were assumed for the purpose of the abovecalculations, but other RIPs are possible, and claimed subject matter isnot limited in this regard.

FIGS. 7-10 depict experimental results (measured intensitydistributions) to illustrate further output beams for various bend radiiof VBC fiber 200 shown in FIG. 2.

In FIG. 7 when VBC fiber 200 is straight, the beam is nearly completelyconfined to confinement region 216. As the bend radius is decreased, theintensity distribution shifts to higher diameters (FIGS. 8-10). FIG. 8depicts the intensity distribution when the bend radius of VBC fiber 200is chosen to shift the intensity distribution preferentially toconfinement region 218. FIG. 9 depicts the experimental results when thebend radius is further reduced and chosen to shift the intensitydistribution outward to confinement region 220 and confinement region218. In FIG. 10, at the smallest bend radius, the beam is nearly a“donut mode”, with most of the intensity in the outermost confinementregion 220.

Despite excitation of the confinement regions from one side at thesplice junction 206, the intensity distributions are nearly symmetricazimuthally because of scrambling within confinement regions as the beampropagates within the VBC fiber 200. Although the beam will typicallyscramble azimuthally as it propagates, various structures orperturbations (e.g., coils) could be included to facilitate thisprocess.

For the fiber parameters used in the experiment shown in FIGS. 7-10,particular confinement regions were not exclusively excited because someintensity was present in multiple confinement regions. This feature mayenable advantageous materials processing applications that are optimizedby having a flatter or distributed beam intensity distribution. Inapplications requiring cleaner excitation of a given confinement region,different fiber RIPs could be employed to enable this feature.

The results shown in FIGS. 7-10 pertain to the particular fibers used inthis experiment, and the details will vary depending on the specifics ofthe implementation. In particular, the spatial profile and divergencedistribution of the output beam and their dependence on bend radius willdepend on the specific RIPs employed, on the splice parameters, and onthe characteristics of the laser source launched into the first fiber.

Different fiber parameters than those shown in FIG. 2 may be used andstill be within the scope of the claimed subject matter. Specifically,different RIPs and core sizes and shapes may be used to facilitatecompatibility with different input beam profiles and to enable differentoutput beam characteristics. Example RIPs for the first length of fiber,in addition to the parabolic-index profile shown in FIG. 2, includeother graded-index profiles, step-index, pedestal designs (i.e., nestedcores with progressively lower refractive indices with increasingdistance from the center of the fiber), and designs with nested coreswith the same refractive index value but with various NA values for thecentral core and the surrounding rings. Example RIPs for the secondlength of fiber, in addition to the profile shown in FIG. 2, includeconfinement fibers with different numbers of confinement regions,non-uniform confinement-region thicknesses, different and/or non-uniformvalues for the thicknesses of the rings surrounding the confinementregions, different and/or non-uniform NA values for the confinementregions, different refractive-index values for the high-index andlow-index portions of the RIP, non-circular confinement regions (such aselliptical, oval, polygonal, square, rectangular, or combinationsthereof), as well as other designs as discussed in further detail withrespect to FIGS. 26-28. Furthermore, VBC fiber 200 and other examples ofa VBC fiber described herein are not restricted to use of two fibers. Insome examples, implementation may include use of one fiber or more thantwo fibers. In some cases, the fiber(s) may not be axially uniform; forexample, they could include fiber Bragg gratings or long-periodgratings, or the diameter could vary along the length of the fiber. Inaddition, the fibers do not have to be azimuthally symmetric, e.g., thecore(s) could have square or polygonal shapes. Various fiber coatings(buffers) may be employed, including high-index or index-matchedcoatings (which strip light at the glass-polymer interface) andlow-index coatings (which guide light by total internal reflection atthe glass-polymer interface). In some examples, multiple fiber coatingsmay be used on VBC fiber 200.

FIGS. 11-16 illustrate cross-sectional views of examples of firstlengths of fiber for enabling adjustment of beam characteristics in aVBC fiber responsive to perturbation of an optical beam propagating inthe first lengths of fiber. Some examples of beam characteristics thatmay be adjusted in the first length of fiber are: beam diameter, beamdivergence distribution, BPP, intensity distribution, luminance, M²factor, NA, optical intensity profile, power density profile, radialbeam position, radiance, spot size, or the like, or any combinationthereof. The first lengths of fiber depicted in FIGS. 11-16 anddescribed below are merely examples and do not provide an exhaustiverecitation of the variety of first lengths of fiber that may be utilizedto enable adjustment of beam characteristics in a VBC fiber assembly.Selection of materials, appropriate RIPs, and other variables for thefirst lengths of fiber illustrated in FIGS. 11-16 at least depend on adesired beam output. A wide variety of fiber variables are contemplatedand are within the scope of the claimed subject matter. Thus, claimedsubject matter is not limited by examples provided herein.

In FIG. 11 first length of fiber 1100 comprises a step-index profile1102. FIG. 12 illustrates a first length of fiber 1200 comprising a“pedestal RIP” (i.e., a core comprising a step-index region surroundedby a larger step-index region) 1202. FIG. 13 illustrates first length offiber 1300 comprising a multiple-pedestal RIP 1302.

FIG. 14A illustrates first length of fiber 1400 comprising agraded-index profile 1418 surrounded by a down-doped region 1404. Whenthe fiber 1400 is perturbed, modes may shift radially outward in fiber1400 (e.g., during bending of fiber 1400). Graded-index profile 1402 maybe designed to promote maintenance or even compression of modal shape.This design may promote adjustment of a beam propagating in fiber 1400to generate a beam having a beam intensity distribution concentrated inan outer perimeter of the fiber (i.e., in a portion of the fiber corethat is displaced from the fiber axis). As described above, when theadjusted beam is coupled into a second length of fiber havingconfinement regions, the intensity distribution of the adjusted beam maybe trapped in the outermost confinement region, providing a donut shapedintensity distribution. A beam spot having a narrow outer confinementregion may be useful to enable certain material processing actions.

FIG. 14B illustrates first length of fiber 1406 comprising agraded-index profile 1414 surrounded by a down-doped region 1408 similarto fiber 1400. However, fiber 1406 includes a divergence structure 1410(a lower-index region) as can be seen in profile 1412. The divergencestructure 1410 is an area of material with a lower refractive index thanthat of the surrounding core. As the beam is launched into first lengthof fiber 1406, refraction from divergence structure 1410 causes the beamdivergence to increase in first length of fiber 1406. The amount ofincreased divergence depends on the amount of spatial overlap of thebeam with the divergence structure 1410 and the magnitude of the indexdifference between the divergence structure 1410 and the core material.Divergence structure 1410 can have a variety of shapes, depending on theinput divergence distribution and desired output divergencedistribution. In an example, divergence structure 1410 has a triangularor graded index shape.

FIG. 15 illustrates a first length of fiber 1500 comprising aparabolic-index central region 1502 surrounded by a constant-indexregion 1504, and the constant-index region 1504 is surrounded by alower-index annular layer 1506. The lower-index annulus 1506 helps guidea beam propagating in fiber 1500. When the propagating beam isperturbed, modes shift radially outward in fiber 1500 (e.g., duringbending of fiber 1500). As one or more modes shift radially outward,parabolic-index region 1502 promotes retention of modal shape. When themodes reach the constant-index region of the RIP 1510, they will becompressed against the low-index ring 1506, which may cause preferentialexcitation of the outermost confinement region in the second fiber (incomparison to the first fiber RIP shown in FIG. 14). In oneimplementation, this fiber design works with a confinement fiber havinga central step-index core and a single annular core. The parabolic-indexportion 1502 of the RIP overlaps with the central step-index core of theconfinement fiber. The constant-index portion 1504 overlaps with theannular core of the confinement fiber. The constant-index portion 1504of the first fiber is intended to make it easier to move the beam intooverlap with the annular core by bending. This fiber design also workswith other designs of the confinement fiber.

FIG. 16 illustrates a first length of fiber 1600 comprising guidingregions 1604, 1606, 1608, and 1616 bounded by lower-index layers 1610,1612, and 1614 where the indexes of the lower-index layers 1610, 1612,and 1614 are stepped or, more generally, do not all have the same value.The stepped-index layers may serve to bound the beam intensity tocertain guiding regions (1604, 1606, 1608, and 1616) when theperturbation assembly 210 (see FIG. 2) acts on the fiber 1600. In thisway, adjusted beam light may be trapped in the guiding regions over arange of perturbation actions (such as over a range of bend radii, arange of bend lengths, a range of micro-bending pressures, and/or arange of acousto-optical signals), allowing for a certain degree ofperturbation tolerance before a beam intensity distribution is shiftedto a more distant radial position in fiber 1600. Thus, variation in beamcharacteristics may be controlled in a step-wise fashion. The radialwidths of the guiding regions 1604, 1606, 1608, and 1616 may be adjustedto achieve a desired ring width, as may be required by an application.Also, a guiding region can have a thicker radial width to facilitatetrapping of a larger fraction of the incoming beam profile if desired.Region 1606 is an example of such a design.

FIGS. 17-21 depict examples of fibers configured to enable maintenanceand/or confinement of adjusted beam characteristics in the second lengthof fiber (e.g., fiber 208). These fiber designs are referred to as“ring-shaped confinement fibers” because they contain a central coresurrounded by annular or ring-shaped cores. These designs are merelyexamples and not an exhaustive recitation of the variety of fiber RIPsthat may be used to enable maintenance and/or confinement of adjustedbeam characteristics within a fiber. Thus, claimed subject matter is notlimited to the examples provided herein. Moreover, any of the firstlengths of fiber described above with respect to FIGS. 11-16 may becombined with any of the second length of fiber described FIGS. 17-21.

FIG. 17 illustrates a cross-sectional view of an example second lengthof fiber for maintaining and/or confining adjusted beam characteristicsin a VBC fiber assembly. As the perturbed beam is coupled from a firstlength of fiber to second length of fiber 1700, the second length offiber 1700 may maintain at least a portion of the beam characteristicsadjusted in response to perturbation in the first length of fiber withinone or more of confinement regions 1704, 1706, and/or 1708. Fiber 1700has a RIP 1702. Each of confinement regions 1704, 1706, and/or 1708 isbounded by a lower index layer 1710 and/or 1712. This design enablessecond length of fiber 1700 to maintain the adjusted beamcharacteristics. As a result, a beam output by fiber 1700 willsubstantially maintain the received adjusted beam as modified in thefirst length of fiber giving the output beam adjusted beamcharacteristics, which may be customized to a processing task or otherapplication.

Similarly, FIG. 18 depicts a cross-sectional view of an example secondlength of fiber 1800 for maintaining and/or confining beamcharacteristics adjusted in response to perturbation in the first lengthof fiber in a VBC fiber assembly. Fiber 1800 has a RIP 1802. However,confinement regions 1808, 1810, and/or 1812 have different thicknessesthan confinement regions 1704, 1706, and 1708. Each of confinementregions 1808, 1810, and/or 1812 is bounded by a lower index layer 1804and/or 1806. Varying the thicknesses of the confinement regions (and/orbarrier regions) enables tailoring or optimization of a confinedadjusted radiance profile by selecting particular radial positionswithin which to confine an adjusted beam.

FIG. 19 depicts a cross-sectional view of an example second length offiber 1900 having a RIP 1902 for maintaining and/or confining anadjusted beam in a VBC fiber assembly configured to provide variablebeam characteristics. In this example, the number and thicknesses ofconfinement regions 1904, 1906, 1908, and 1910 are different from fiber1700 and 1800 and the barrier layers 1912, 1914, and 1916 are of variedthicknesses as well. Furthermore, confinement regions 1904, 1906, 1908,and 1910 have different indexes of refraction and barrier layers 1912,1914, and 1916 have different indexes of refraction as well. This designmay further enable a more granular or optimized tailoring of theconfinement and/or maintenance of an adjusted beam radiance toparticular radial locations within fiber 1900. As the perturbed beam islaunched from a first length of fiber to second length of fiber 1900 themodified beam characteristics of the beam (having an adjusted intensitydistribution, radial position, and/or divergence angle, or the like, ora combination thereof) is confined within a specific radius by one ormore of confinement regions 1904, 1906, 1908 and/or 1910 of secondlength of fiber 1900.

As noted previously, the divergence angle of a beam may be conserved oradjusted and then conserved in the second length of fiber. There are avariety of methods to change the divergence angle of a beam. Thefollowing are examples of fibers configured to enable adjustment of thedivergence angle of a beam propagating from a first length of fiber to asecond length of fiber in a fiber assembly for varying beamcharacteristics. However, these are merely examples and not anexhaustive recitation of the variety of methods that may be used toenable adjustment of divergence of a beam. Thus, claimed subject matteris not limited to the examples provided herein.

FIG. 20 depicts a cross-sectional view of an example second length offiber 2000 having RIP 2002 for modifying, maintaining, and/or confiningbeam characteristics adjusted in response to perturbation in the firstlength of fiber. In this example, second length of fiber 2000 is similarto the previously described second lengths of fiber and forms a portionof the VBC fiber assembly for delivering variable beam characteristicsas discussed above. There are three confinement regions 2004, 2006, and2008 and three barrier layers 2010, 2012, and 2016. Second length offiber 2000 also has a divergence structure 2014 situated within theconfinement region 2006. The divergence structure 2014 is an area ofmaterial with a lower refractive index than that of the surroundingconfinement region. As the beam is launched into second length of fiber2000 refraction from divergence structure 2014 causes the beamdivergence to increase in second length of fiber 2000. The amount ofincreased divergence depends on the amount of spatial overlap of thebeam with the divergence structure 2014 and the magnitude of the indexdifference between the divergence structure 2014 and the core material.By adjusting the radial position of the beam near the launch point intothe second length of fiber 2000, the divergence distribution may bevaried. The adjusted divergence of the beam is conserved in fiber 2000,which is configured to deliver the adjusted beam to the process head,another optical system (e.g., fiber-to-fiber coupler or fiber-to-fiberswitch), the work piece, or the like, or a combination thereof. In anexample, divergence structure 2014 may have an index dip of about10⁻⁵-3×10⁻² with respect to the surrounding material. Other values ofthe index dip may be employed within the scope of this disclosure andclaimed subject matter is not so limited.

FIG. 21 depicts a cross-sectional view of an example second length offiber 2100 having a RIP 2102 for modifying, maintaining, and/orconfining beam characteristics adjusted in response to perturbation inthe first length of fiber. Second length of fiber 2100 forms a portionof a VBC fiber assembly for delivering a beam having variablecharacteristics. In this example, there are three confinement regions2104, 2106, and 2108 and three barrier layers 2110, 2112, and 2116.Second length of fiber 2100 also has a plurality of divergencestructures 2114 and 2118. The divergence structures 2114 and 2118 areareas of graded lower index material. As the beam is launched from thefirst length fiber into second length of fiber 2100, refraction fromdivergence structures 2114 and 2118 causes the beam divergence toincrease. The amount of increased divergence depends on the amount ofspatial overlap of the beam with the divergence structure and themagnitude of the index difference between the divergence structure 2114and/or 2118 and the surrounding core material of confinement regions2106 and 2104 respectively. By adjusting the radial position of the beamnear the launch point into the second length of fiber 2100, thedivergence distribution may be varied. The design shown in FIG. 21allows the intensity distribution and the divergence distribution to bevaried somewhat independently by selecting both a particular confinementregion and the divergence distribution within that conferment region(because each confinement region may include a divergence structure).The adjusted divergence of the beam is conserved in fiber 2100, which isconfigured to deliver the adjusted beam to the process head, anotheroptical system, or the work piece. Forming the divergence structures2114 and 2118 with a graded or non-constant index enables tuning of thedivergence profile of the beam propagating in fiber 2100. An adjustedbeam characteristic such as a radiance profile and/or divergence profilemay be conserved as it is delivered to a process head by the secondfiber. Alternatively, an adjusted beam characteristic such as a radianceprofile and/or divergence profile may be conserved or further adjustedas it is routed by the second fiber through a fiber-to-fiber coupler(FFC) and/or fiber-to-fiber switch (FFS) and to a process fiber, whichdelivers the beam to the process head or the work piece.

FIGS. 26-28 are cross-sectional views illustrating examples of fibersand fiber RIPs configured to enable maintenance and/or confinement ofadjusted beam characteristics of a beam propagating in an azimuthallyasymmetric second length of fiber wherein the beam characteristics areadjusted responsive to perturbation of a first length of fiber coupledto the second length of fiber and/or perturbation of the beam by aperturbation device 110. These azimuthally asymmetric designs are merelyexamples and are not an exhaustive recitation of the variety of fiberRIPs that may be used to enable maintenance and/or confinement ofadjusted beam characteristics within an azimuthally asymmetric fiber.Thus, claimed subject matter is not limited to the examples providedherein. Moreover, any of a variety of first lengths of fiber (e.g., likethose described above) may be combined with any azimuthally asymmetricsecond length of fiber (e.g., like those described in FIGS. 26-28).

FIG. 26 illustrates RIPs at various azimuthal angles of a cross-sectionthrough an elliptical fiber 2600. At a first azimuthal angle 2602, fiber2600 has a first RIP 2604. At a second azimuthal angle 2606 that isrotated 45° from first azimuthal angle 2602, fiber 2600 has a second RIP2608. At a third azimuthal angle 2610 that is rotated another 45° fromsecond azimuthal angle 2606, fiber 2600 has a third RIP 2612. First,second and third RIPs 2604, 2608 and 2612 are all different.

FIG. 27 illustrates RIPs at various azimuthal angles of a cross-sectionthrough a multicore fiber 2700. At a first azimuthal angle 2702, fiber2700 has a first RIP 2704. At a second azimuthal angle 2706, fiber 2700has a second RIP 2708. First and second RIPs 2704 and 2708 aredifferent. In an example, perturbation device 110 may act in multipleplanes in order to launch the adjusted beam into different regions of anazimuthally asymmetric second fiber.

FIG. 28 illustrates RIPs at various azimuthal angles of a cross-sectionthrough a fiber 2800 having at least one crescent shaped core. In somecases, the corners of the crescent may be rounded, flattened, orotherwise shaped, which may minimize optical loss. At a first azimuthalangle 2802, fiber 2800 has a first RIP 2804. At a second azimuthal angle2806, fiber 2800 has a second RIP 2808. First and second RIPs 2804 and2808 are different.

FIG. 22A illustrates an example of a laser system 2200 including a VBCfiber assembly 2202 configured to provide variable beam characteristics.VBC fiber assembly 2202 comprises a first length of fiber 104, secondlength of fiber 108, and a perturbation device 110. VBC fiber assembly2202 is disposed between feeding fiber 2212 (i.e., the output fiber fromthe laser source) and VBC delivery fiber 2240. VBC delivery fiber 2240may comprise second length of fiber 108 or an extension of second lengthof fiber 108 that modifies, maintains, and/or confines adjusted beamcharacteristics. Beam 2210 is coupled into VBC fiber assembly 2202 viafeeding fiber 2212. Fiber assembly 2202 is configured to vary thecharacteristics of beam 2210 in accordance with the various examplesdescribed above. The output of fiber assembly 2202 is adjusted beam 2214which is coupled into VBC delivery fiber 2240. VBC delivery fiber 2240delivers adjusted beam 2214 to free-space optics assembly 2208, whichthen couples beam 2214 into a process fiber 2204. Adjusted beam 2214 isthen delivered to process head 2206 by process fiber 2204. The processhead can include guided wave optics (such as fibers and fiber coupler),free space optics such as lenses, mirrors, optical filters, diffractiongratings), beam scan assemblies such as galvanometer scanners, polygonalmirror scanners, or other scanning systems that are used to shape thebeam 2214 and deliver the shaped beam to a workpiece.

In laser system 2200, one or more of the free-space optics of assembly2208 may be disposed in an FFC or other beam coupler 2216 to perform avariety of optical manipulations of an adjusted beam 2214 (representedin FIG. 22A with different dashing than beam 2210). For example,free-space optics assembly 2208 may preserve the adjusted beamcharacteristics of beam 2214. Process fiber 2204 may have the same RIPas VBC delivery fiber 2240. Thus, the adjusted beam characteristics ofadjusted beam 2214 may be preserved all the way to process head 2206.Process fiber 2204 may comprise a RIP similar to any of the secondlengths of fiber described above, including confinement regions.

FFCs can include one, two, or more lenses, but in typical examples, twolenses having the same nominal focal length are used, producing unitmagnification. In most practical examples, magnification produced withan FFC is between 0.8 and 1.2, which corresponds to a ratio of focallengths.

Alternatively, as illustrated in FIG. 22B, free-space optics assembly2208 may change the adjusted beam characteristics of beam 2214 by, forexample, increasing or decreasing the divergence and/or the spot size ofbeam 2214 (e.g., by magnifying or demagnifying beam 2214) and/orotherwise further modifying adjusted beam 2214. Furthermore, processfiber 2204 may have a different RIP than VBC delivery fiber 2240.Accordingly, the RIP of process fiber 2204 may be selected to preserveadditional adjustment of adjusted beam 2214 made by the free-spaceoptics of assembly 2208 to generate a twice adjusted beam 2224(represented in FIG. 22B with different dashing than beam 2214).

FIG. 23 illustrates an example of a laser system 2300 including VBCfiber assembly 2302 disposed between feeding fiber 2312 and VBC deliveryfiber 2340. During operation, beam 2310 is coupled into VBC fiberassembly 2302 via feeding fiber 2312. Fiber assembly 2302 includes afirst length of fiber 104, second length of fiber 108, and aperturbation device 110 and is configured to vary characteristics ofbeam 2310 in accordance with the various examples described above. Fiberassembly 2302 generates adjusted beam 2314 output by VBC delivery fiber2340. VBC delivery fiber 2340 comprises a second length of fiber 108 offiber for modifying, maintaining, and/or confining adjusted beamcharacteristics in a fiber assembly 2302 in accordance with the variousexamples described above (see FIGS. 17-21, for example). VBC deliveryfiber 2340 couples adjusted beam 2314 into beam switch (FFS) 2332, whichthen couples its various output beams to one or more of multiple processfibers 2304, 2320, and 2322. Process fibers 2304, 2320, and 2322 deliveradjusted beams 2314, 2328, and 2330 to respective process heads 2306,2324, and 2326.

In an example, beam switch 2332 includes one or more sets of free-spaceoptics 2308, 2316, and 2318 configured to perform a variety of opticalmanipulations of adjusted beam 2314. Free-space optics 2308, 2316, and2318 may preserve or vary adjusted beam characteristics of beam 2314.Thus, adjusted beam 2314 may be maintained by the free-space optics oradjusted further. Process fibers 2304, 2320, and 2322 may have the sameor a different RIP as VBC delivery fiber 2340, depending on whether itis desirable to preserve or further modify a beam passing from thefree-space optics assemblies 2308, 2316, and 2318 to respective processfibers 2304, 2320, and 2322. In other examples, one or more beamportions of beam 2310 are coupled to a workpiece without adjustment, ordifferent beam portions are coupled to respective VBC fiber assembliesso that beam portions associated with a plurality of beamcharacteristics can be provided for simultaneous workpiece processing.Alternatively, beam 2310 can be switched to one or more of a set of VBCfiber assemblies.

Routing adjusted beam 2314 through any of free-space optics assemblies2308, 2316, and 2318 enables delivery of a variety of additionallyadjusted beams to process heads 2206, 2324, and 2326. Therefore, lasersystem 2300 provides additional degrees of freedom for varying thecharacteristics of a beam, as well as switching the beam between processheads (“time sharing”) and/or delivering the beam to multiple processheads simultaneously (“power sharing”).

For example, free-space optics in beam switch 2332 may direct adjustedbeam 2314 to free-space optics assembly 2316 configured to preserve theadjusted characteristics of beam 2314. Process fiber 2304 may have thesame RIP as VBC delivery fiber 2340. Thus, the beam delivered to processhead 2306 will be a preserved adjusted beam 2314.

In another example, beam switch 2332 may direct adjusted beam 2314 tofree-space optics assembly 2318 configured to preserve the adjustedcharacteristics of adjusted beam 2314. Process fiber 2320 may have adifferent RIP than VBC delivery fiber 2340 and may be configured withdivergence altering structures as described with respect to FIGS. 20 and21 to provide additional adjustments to the divergence distribution ofbeam 2314. Thus, the beam delivered to process head 2324 will be a twiceadjusted beam 2328 having a different beam divergence profile thanadjusted beam 2314.

Process fibers 2304, 2320, and/or 2322 may comprise a RIP similar to anyof the second lengths of fiber described above, including confinementregions or a wide variety of other RIPs, and claimed subject matter isnot limited in this regard.

In yet another example, free-space optics switch 2332 may directadjusted beam 2314 to free-space optics assembly 2308 configured tochange the beam characteristics of adjusted beam 2314. Process fiber2322 may have a different RIP than VBC delivery fiber 2340 and may beconfigured to preserve (or alternatively further modify) the new furtheradjusted characteristics of beam 2314. Thus, the beam delivered toprocess head 2326 will be a twice adjusted beam 2330 having differentbeam characteristics (due to the adjusted divergence profile and/orintensity profile) than adjusted beam 2314.

In FIGS. 22A, 22B, and 23, the optics in the FFC or FFS may adjust thespatial profile and/or divergence profile by magnifying or demagnifyingthe beam 2214 before launching into the process fiber. They may alsoadjust the spatial profile and/or divergence profile via other opticaltransformations. They may also adjust the launch position into theprocess fiber. These methods may be used alone or in combination.

FIGS. 22A, 22B, and 23 merely provide examples of combinations ofadjustments to beam characteristics using free-space optics and variouscombinations of fiber RIPs to preserve or modify adjusted beams 2214 and2314. The examples provided above are not exhaustive and are meant forillustrative purposes only. Thus, claimed subject matter is not limitedin this regard.

FIG. 24 illustrates various examples of perturbation devices, assembliesor methods (for simplicity referred to collectively herein as“perturbation device 110”) for perturbing a VBC fiber 200 and/or anoptical beam propagating in VBC fiber 200 according to various examplesprovided herein. Perturbation device 110 may be any of a variety ofdevices, methods, and/or assemblies configured to enable adjustment ofbeam characteristics of a beam propagating in VBC fiber 200. In anexample, perturbation device 110 may be a mandrel 2402, a micro-bend2404 in the VBC fiber, flexible tubing 2406, an acousto-optic transducer2408, a thermal device 2410, a piezo-electric device 2412, a grating2414, a clamp 2416 (or other fastener), or the like, or any combinationthereof. These are merely examples of perturbation devices 100 and notan exhaustive listing of perturbation devices 100 and claimed subjectmatter is not limited in this regard.

Mandrel 2402 may be used to perturb VBC fiber 200 by providing a formabout which VBC fiber 200 may be bent. As discussed above, reducing thebend radius of VBC fiber 200 moves the intensity distribution of thebeam radially outward. In some examples, mandrel 2402 may be stepped orconically shaped to provide discrete bend radii levels. Alternatively,mandrel 2402 may comprise a cone shape without steps to providecontinuous bend radii for more granular control of the bend radius. Theradius of curvature of mandrel 2402 may be constant (e.g., a cylindricalform) or non-constant (e.g., an oval-shaped form). Similarly, flexibletubing 2406, clamps 2416 (or other varieties of fasteners), or rollers250 may be used to guide and control the bending of VBC fiber 200 aboutmandrel 2402. Furthermore, changing the length over which the fiber isbent at a particular bend radius also may modify the intensitydistribution of the beam. VBC fiber 200 and mandrel 2402 may beconfigured to change the intensity distribution within the first fiberpredictably (e.g., in proportion to the length over which the fiber isbent and/or the bend radius). Rollers 250 may move up and down along atrack 2442 on platform 2434 to change the bend radius of VBC fiber 200.

Clamps 2416 (or other fasteners) may be used to guide and control thebending of VBC fiber 200 with or without a mandrel 2402. Clamps 2416 maymove up and down along a track 2442 or platform 2446. Clamps 2416 mayalso swivel to change bend radius, tension, or direction of VBC fiber200. Controller 2448 may control the movement of clamps 2416.

In another example, perturbation device 110 may be flexible tubing 2406and may guide bending of VBC fiber 200 with or without a mandrel 2402.Flexible tubing 2406 may encase VBC fiber 200. Tubing 2406 may be madeof a variety of materials and may be manipulated using piezoelectrictransducers controlled by controller 2444. In another example, clamps orother fasteners may be used to move flexible tubing 2406.

Micro-bend 2404 in VBC fiber is a local perturbation caused by lateralmechanical stress on the fiber. Micro-bending can cause mode couplingand/or transitions from one confinement region to another confinementregion within a fiber, resulting in varied beam characteristics of thebeam propagating in a VBC fiber 200. Mechanical stress may be applied byan actuator 2436 that is controlled by controller 2440. However, this ismerely an example of a method for inducing mechanical stress in fiber200 and claimed subject matter is not limited in this regard.

Acousto-optic transducer (AOT) 2408 may be used to induce perturbationof a beam propagating in the VBC fiber using an acoustic wave. Theperturbation is caused by the modification of the refractive index ofthe fiber by the oscillating mechanical pressure of an acoustic wave.The period and strength of the acoustic wave are related to the acousticwave frequency and amplitude, allowing dynamic control of the acousticperturbation. Thus, a perturbation assembly 110 including AOT 2408 maybe configured to vary the beam characteristics of a beam propagating inthe fiber. In an example, piezo-electric transducer 2418 may create theacoustic wave and may be controlled by controller or driver 2420. Theacoustic wave induced in AOT 2408 may be modulated to change and/orcontrol the beam characteristics of the optical beam in VBC 200 inreal-time. However, this is merely an example of a method for creatingand controlling an AOT 2408 and claimed subject matter is not limited inthis regard.

Thermal device 2410 may be used to induce perturbation of a beampropagating in VBC fiber using heat. The perturbation is caused by themodification of the RIP of the fiber induced by heat. Perturbation maybe dynamically controlled by controlling an amount of heat transferredto the fiber and the length over which the heat is applied. Thus, aperturbation assembly 110 including thermal device 2410 may beconfigured to vary a range of beam characteristics. Thermal device 2410may be controlled by controller 2450.

Piezo-electric transducer 2412 may be used to induce perturbation of abeam propagating in a VBC fiber using piezoelectric action. Theperturbation is caused by the modification of the RIP of the fiberinduced by a piezoelectric material attached to the fiber. Thepiezoelectric material in the form of a jacket around the bare fiber mayapply tension or compression to the fiber, modifying its refractiveindex via the resulting changes in density. Perturbation may bedynamically controlled by controlling a voltage to the piezo-electricdevice 2412. Thus, a perturbation assembly 110 including piezo-electrictransducer 2412 may be configured to vary the beam characteristics overa particular range.

In an example, piezo-electric transducer 2412 may be configured todisplace VBC fiber 200 in a variety of directions (e.g., axially,radially, and/or laterally) depending on a variety of factors, includinghow the piezo-electric transducer 2412 is attached to VBC fiber 200, thedirection of the polarization of the piezo-electric materials, theapplied voltage, etc. Additionally, bending of VBC fiber 200 is possibleusing the piezo-electric transducer 2412. For example, driving a lengthof piezo-electric material having multiple segments comprising opposingelectrodes can cause a piezoelectric transducer 2412 to bend in alateral direction. Voltage applied to piezoelectric transducer 2412 byelectrode 2424 may be controlled by controller 2422 to controldisplacement of VBC fiber 200. Displacement may be modulated to changeand/or control the beam characteristics of the optical beam in VBC 200in real-time. However, this is merely an example of a method ofcontrolling displacement of a VBC fiber 200 using a piezo-electrictransducer 2412 and claimed subject matter is not limited in thisregard.

Gratings 2414 may be used to induce perturbation of a beam propagatingin a VBC fiber 200. A grating 2414 can be written into a fiber byinscribing a periodic variation of the refractive index into the core.Gratings 2414 such as fiber Bragg gratings can operate as opticalfilters or as reflectors. A long-period grating can induce transitionsamong co-propagating fiber modes. The radiance, intensity profile,and/or divergence profile of a beam comprised of one or more modes canthus be adjusted using a long-period grating to couple one or more ofthe original modes to one or more different modes having differentradiance and/or divergence profiles. Adjustment is achieved by varyingthe periodicity or amplitude of the refractive index grating. Methodssuch as varying the temperature, bend radius, and/or length (e.g.,stretching) of the fiber Bragg grating can be used for such adjustment.VBC fiber 200 having gratings 2414 may be coupled to stage 2426. Stage2426 may be configured to execute any of a variety of functions and maybe controlled by controller 2428. For example, stage 2426 may be coupledto VBC fiber 200 with fasteners 2430 and may be configured to stretchand/or bend VBC fiber 200 using fasteners 2430 for leverage. Stage 2426may have an embedded thermal device and may change the temperature ofVBC fiber 200.

FIG. 25 illustrates an example process 2500 for adjusting and/ormaintaining beam characteristics within a fiber without the use offree-space optics to adjust the beam characteristics. In block 2502, afirst length of fiber and/or an optical beam are perturbed to adjust oneor more optical beam characteristics. Process 2500 moves to block 2504,where the optical beam is launched into a second length of fiber.Process 2500 moves to block 2506, where the optical beam having theadjusted beam characteristics is propagated in the second length offiber. Process 2500 moves to block 2508, where at least a portion of theone or more beam characteristics of the optical beam are maintainedwithin one or more confinement regions of the second length of fiber.The first and second lengths of fiber may be comprised of the samefiber, or they may be different fibers.

With reference to FIGS.29A-29C, a variable beam characteristics (VBC)apparatus 2900 includes a disc 2902. The disc 2902 is a perturbationassembly having circular, elliptical, or other curved cross-sectiondefining a perimeter surface 2904 that serves as a fiber bending orfiber shaping surface. Fiber guides 2906, 2908 are situated at theperimeter surface 2904 to urge a section of a first fiber 2910 towardthe perimeter surface 2904. The fiber guides 2906, 2908 are secured tospokes 2907, 2909 that are connected to permit the fiber guides 2906,2908 be rotatable about an axis 2912. A separation of the guides 2906,2908 along the perimeter surface 2904 defines an angle 0 that isassociated with a length of a section of the first fiber 2910 thatconforms to or is urged to contact the perimeter surface 2904. Rotationof one or both of the guides 2906, 2908 permits selection of a suitablelength. In some examples, a fiber is secured to a guide such as theguide 2908, and rotation of the guide wraps a fiber about a fiberbending surface, thereby selecting a fiber length to be bent based onrotation of a guide. In such examples, a tension mechanism can beprovided so that the fiber unwinds from a fiber bending surface as theguide rotates to unwrap the fiber.

The guides 2906, 2908 can include surfaces that press fibers toward thefiber bending surface. For example, the guides 2906, 2908 can be made ofor include an elastic portion of rubber, foam, cloth, fibers, or othermaterial than can be urged against a fiber without compromising fiberintegrity and to accommodate sharp surface irregularities that coulddamage fibers. The fiber bending surface such as the perimeter surface2904 can be provided with a similar material along the entire surface oronly at portions expected to be used in conforming fibers.Alternatively, the guides 2906, 2908 can include grooves such as agroove 2916 that retains a fiber and may or may not press the fiberagainst the fiber bending surface. For guides that are rotatable,grooves may extend around the entire perimeter so that a fiber isretained in the groove as the guide rotates and travels along the fiberbending surface.

The first fiber 2910 is typically connected to a second fiber 2920 witha splice 2918 such as a fusion splice (shown in possible two locationsin FIG. 29A). In some examples, a single fiber can be used, butgenerally two different fibers are used having different refractiveindex profiles. The guides 2906, 2908 then urge a section of the secondfiber into a bent path along the perimeter surface 2904 (along with thesplice 2918). In some examples, the spokes 2907, 2909 are rigid, but inother examples, elastic members such as springs can be used (or spokescan include an elastic portion) so that the guides 2906, 2908 are pulledtoward the perimeter surface 2904. In many practical examples, only oneguide is used, but one, two, three, or more can be used to selectportions of one or more fibers to be conformed to the fiber bendingsurface 2904. For example, sections of the first fiber 2910 and thesecond fiber 2920 can be independently selected to be urged toward theperimeter surface using respective pairs of guides.

Locations of the guides 2906, 2908 can be controlled using motor 2930that is coupled to the spokes 2907, 2909 to rotate to establish theangle θ. A controller 2932 is coupled to the motor 2930 so that theguides 2906, 2908 can be computer or processor controlled, or controlledmanually. In some examples, the controller 2932 includes anon-transitory computer readable medium that includes a calibrationtable in which the angle θ and associated beam characteristics arestored. In systems having multiple guides, each can be arranged to beindependently moved, and sections of one or more fibers can be selected.

In the example of FIGS. 29A-29C, a single bend radius is associated witha fiber bending surface, but in other examples, series of different bendradii can be used, each defined with a corresponding step formed as, forexample, a portion of a cylinder, or on a tapered surface such as a coneor portion thereof. Arcuate or other curved surfaces can be used aswell. Guides can be situated to direct fibers to a fiber bending orshaping surface having a particular curvature as well as selecting alength of fiber to be shaped into that curvature. Fiber sections can bebent at a plurality of surface areas having associated curvatures andsection lengths can be varied for each curvature. Cylindrical curvaturesare shown in FIGS. 29A-29C, but curvatures along multiple directionssuch as spherical or ellipsoidal curvatures can be used. The perimetersurface 2904 is an exterior surface of the disc 2902, but in otherexamples, interior surfaces of rings, hollow cylinders, or other shapescan be used as fiber bending or shaping surfaces, and guides situated toadjust fiber shape with respect to such interior surfaces.

In the disclosed examples, an optical fiber that includes a length of afirst optical fiber and a second optical fiber that are fusion splicedis bent at or near the fusion splice so as to vary a spatial beamprofile or other beam characteristic produced in the first fiber or thesecond fiber. More efficient adjustment of spatial beam profile istypically achieved if the fusion splice is included in the bent portionof the fiber. However, the fusion splice can be located sufficientlyclose to the bent portion. Typically, the fusion splice should besituated within a length of less than about 2, 5, 10, 50, 100, 500, or1000 times a core diameter of either fiber. Sufficient fiber lengths canalso depend on fiber numerical aperture as well. One possibleexplanation for the utility of bending either the first fiber or thesecond fiber is that bending of a fiber near a launch point, which is atthe spliced junction 2918, can produce a variable spatial beam profilethat propagates some distance before collapsing to an original beamshape. In a receiving (second) fiber, bending near a splice can perturba spatial power distribution from the launching (first) fiber, and thusvariably couple the received power into a selected spatial powerdistribution. The disclosure is not limited to operation in accordancewith operation in this way, and this explanation is only provided as onepotential explanation for convenience.

In FIG. 29A, the perturbation assembly disc 2902 is disposed proximal tothe spliced junction 2918. Alternatively, a perturbation assembly maynot be disposed near a splice. Moreover, a splice may not be needed atall, for example the fiber 2910 may be a single fiber, a first length offiber and second length of fiber could be spaced apart, or secured witha small gap (air-spaced or filled with an optical material, such asoptical cement or an index-matching material).

In some examples, the bend radius of a fiber is changed from a firstbend radius R₁ to a second bend radius R₂ by using a stepped mandrel ora cone in a perturbation assembly. Fiber portions having different bendradii can be independently selected. Changing a bend radius of a fibermay change the radial beam position, divergence angle, and/or radianceprofile, or other beam characteristics of a beam within the fiber.

In an example shown in a sectional view in FIG. 30, a disk 3002 definesa perimeter (fiber bending) surface 3004 that is provided with grooves3010, 3011. Typically, the disk 3002 includes a central bore 3006 forinsertion of a rotatable shaft (not shown). A guide 3008 includesprotrusions 3016, 3017 that can be inserted in the grooves 3010, 3011 sothat the guide 3008 is movable along the perimeter surface 3004. A fiber3014 is shown situated in a groove 3015 in the guide 3008. In otherexamples, guides can have dovetail shaped protrusions to fit intocorrespond grooves in a disk or other support. Alternatively, groovescan be provided in the guide, and protrusions in the disk, or anycombination thereof as may be convenient.

With reference to FIG. 31, a VBC apparatus 3100 includes an ellipsoidaldisk 3102 having a perimeter (fiber bending) surface 3104. Guides 3106,3107 are situated to select a length of a fiber 3108 that conforms tothe fiber bending surface 3104. As shown, the guide 3106 is fixed withrespect to the perimeter surface 3104, and the guide 3107 is configuredto be movable along the perimeter surface 3104. In the example of FIG.31, the guide 3107 is secured with an elastic member 3110 so as to berotatable about an axis 3112. The perimeter surface 3104 is defined byan ellipse and thus has a varying radius of curvature, and the elasticmember 3110 is selected to permit the guide 3107 to accommodate varyingdistances from the axis 3112 to the perimeter surface 3104.

FIG. 32 illustrates an additional fiber bending surface 3202 that isformed on a substrate 3200. A surface 3206 opposite the fiber bendingsurface 3202 can be planar, or have a convex or concave curvature. Aguide 3208 is situated to urge a fiber against the fiber bending surface3202, and one, two, three, or more such guides can be used. As discussedabove, the guide 3208 can be retained by a groove and be slidable, orcan be coupled to an elastic member that urges the guide 3208 toward thefiber bending surface 3202. The fiber bending surface 3202 can havevarious simple or complex curvatures, and can be convex, concave, orplanar in at least some portions. The guide 3208 can be spherical orcylindrical and arranged to roll along the fiber bending surface 3204.In some examples, the guide 3208 is situated to urge a fiber 3210 tocontact the fiber bending surface 3202, to change a bend angle of thefiber 3210, or bend the fiber 3210 while leaving a gap 3212 between thefiber 3210 and the fiber bending surface 3202 proximate the guide 3208.

Referring to FIGS. 33A-33B, a guide 3304 is situated to urge a fiber3306 toward a fiber bending surface 3308. The fiber 3306 can be securedwith respect to the fiber bending surface 3308 with a clip 3310 orotherwise fixed so that a length of fiber conformed to the fiber bendingsurface 3208 is determined by a position of the guide 3304. As shown inthe sectional view of FIG. 33B, the fiber 3306 is retained in a channel3312, and the guide 3304 includes protrusions 3320, 3321 that correspondto grooves 3330, 3331 in the fiber bending surface 3308.

With reference to FIG. 34, a section 3402 of a disk defines a fiberbending surface 3404. A clamp 3406 secures a fiber 3408 to the fiberbending surface 3404 and a guide 3410 is movable along the fiber bendingsurface 3404 to control a fiber length that is urged toward the fiberbending surface 3404. The guide 3410 can move along the surface ingrooves and/or be secured to an axis that permits rotation. As shown inFIG. 35, a portion 3502 of ring defines a fiber bending surface 3504. Aclamp 3506 and a guide 3510 are provided to adjust a fiber length thatis conformed to the fiber bending surface 3504. The guide 3510 can beslidable along the fiber bending surface 3504 in grooves or otherwise,or coupled to a spoke to rotate along an axis. In some examples, a fiberbending surface is rotatable or otherwise adjustable so that aseparation of a clamp fixed with respect to the fiber bending surfaceand a guide is adjustable. For example, as shown in FIG. 35, a spoke3512 can permit movement of the guide 3510 along the fiber bendingsurface 3504 and/or a spoke 3514 can be coupled to permit rotation ofthe ring 3502 with respect to the guide 3510. Such rotation or movementof a fiber bending surface can be accomplished by rotation of a disk,cylinder, or other shape that defines the fiber bending surface.

As shown in FIG. 36, a VBC apparatus 3600 includes a flexible plate 3602that is situated to be flexed against fixed supports 3604, 3606 by alinear actuator 3608 that urges a bearing 3610 toward the flexible plate3602. A fiber 3612 is secured to the flexible plate 3602 or otherwisesituated so as to bend in response to flexing of the flexible plate3602.

FIGS. 37A-37B illustrate a spool 3700 that includes a groove or channel3704 that is configured to retain one or more loops of a fiber 3702.Rotation of the spool 3700 (or the fiber about the spool 3700) permitsadjustment of a beam perturbation applied by the fiber 3702. Otherarrangements can be provided that permit varying a number of wraps of afiber on a substrate, and typically a section of a cylinder can suffice.A controller is generally provided to select a number of wraps (turns)by controlling a stepper motor or other motor, but in some examples, thenumber of turns can be adjusted manually. While it may be convenientthat the fiber 3702 contact a radially innermost portion of the groove3704, this is not required.

With reference to FIGS. 38A-38B, a VBC device 3800 includes a cylinder3804 that is situated to press a fiber loop 3802 towards a first jaw3806 and a second jaw 3808 in response to translation of a rod 3812 thatis secured to the cylinder 3804. One or more springs such asrepresentative spring 3810 are situated to urge one or both of the jaws3806, 3808 toward the fiber 3802 and the cylinder 3804. FIG. 38A showsthe fiber loop 3802 without deformation for convenient illustration;with the configuration of FIG. 38B, substantial bending of the fiberloop 3802 would be obtained. Various shapes can be used to press thefiber loop 3802 such as cylindrical, spherical, ellipsoidal, arcuate, orother shapes, and a cylinder is shown for convenient illustration.

FIGS. 39A-39D illustrate fiber shape with various engagements of themechanism of FIGS. 38A-38B. In FIG. 39A, a fiber remains in a loop 3900without bending or deformation. FIGS. 39B-39C show fiber sections 3902,3904, 3906 that contact the jaws 3806, 3808 and the cylinder 3804 asengagement of the mechanism is increased. The shape of the loop 3900changes as well.

FIG. 40 illustrates a VBC apparatus 4000 for perturbing beamcharacteristics that includes a first set 4002 and a second set 4004 ofcylinders or other suitable shapes that are situated opposite eachother. A fiber 4008 is situated between the first set 4002 and thesecond set 4004 so as to be bent or deformed as the first set 4002 andthe second set 3004 are urged toward each other. In FIG. 40, cylindersof the same shape are shown, but one or more of the cylinders of eitherset can have different diameters, and different shapes can be used foreach surface of each set.

A plurality of fiber shaping surfaces can be defined on a singlesubstrate, if convenient, as shown in FIG. 41. A plate 4100 includeselliptical or other protrusions 4101, 4102, 4103, 4104 that providefiber shaping surfaces. Cylindrical, arcuate, spherical, parabolic, orother shapes can be used.

FIG. 42 illustrates a VBC apparatus 4200 that is similar to that of FIG.36 but in which a flexible plate 4202 is pulled against stops 4204, 4206with a linear actuator 4208 that is coupled to the flexible plate 4202with an elastic or rigid coupling 4210. A fiber 4212 is situated toconform to a shape of the flexible plate 4202.

In a further example shown in FIGS. 43A-43B, a beam perturbationmechanism 4300 includes a cylinder 4304 having a central bore 4306 thatcan accommodate a drive shaft. An outer surface 4305 of the cylinder4304 serves as a fiber shaping surface. In FIG. 43B, a fiber 4302 isshown as having been wrapped about the cylinder 4304 several times.Rotation of the cylinder 4304 can be used to provide a selected beamperturbation, either manually, or with a processor-based control systemthat can store beam perturbation characteristics as a function ofrotation angle in one or more non-transitory computer-readable media.

FIGS. 44A-44B illustrate a VBC device 4400 that includes a substrate4402 formed at least in part of an ionic polymer composite (IPC) andhaving a first major surface 4404 and second major surface 4405.Electrodes 4406, 4408 are situated on or at the first major surface 4404and the second major surface 4405, respectively. In some cases there areintervening layers such as non-conductive layers, protective layers, orother layers needed for fabrication or use, but such layers are notshown. A serpentine fiber loop 4410 is secured to the first majorsurface 4404 and is shaped to have elongated portions such as elongatedportion 4411 that extends along an X-axis of a right handed Cartesiancoordinate system 4450. As shown in the sectional view of FIG. 44B,application of an electric field to the substrate 4402 in response to avoltage applied to the electrodes 4406, 4408 produces a Z-directeddeformation so that the first major surface 4404 is bowed or bent assurface 4404A; such deformation produces beam perturbations in the fiberloop 4410. Other deformations in other directions can be produced, andstraight fiber lengths, circular loops, partial loops, serpentinelengths, and other arrangements of fibers can be oriented on either thefirst major surface 4404 or the second major surface 4405 along theX-direction, the Y-direction, or arbitrarily oriented.

In another example illustrated in FIG. 45, a VBC device 4500 includes anIPC substrate 4502 to which fiber serpentine loops 4504, 4505 (orcircular loops or fibers arranged in other shapes) are secured so as tobe subject to flexing of the IPC substrate 4502. Electrodes such aselectrode 4506 are provided at ends of the IPC substrate 4502, but canbe situated in other portions or cover the substrate 4502. Fiber ends4510, 4511 can be used to couple optical beams into and out of the beamperturbation device 4500. As in other examples discussed above, thefiber serpentine loops 4504, 4505 can be of a single fiber (a firstfiber) or a first fiber and a second fiber with a splice.

FIG. 46 illustrates a VBC system 4600 that includes input optics 4601that couple one or more beams to a beam perturbation device 4602 andoutput optics 4604 which receive one or more perturbed beams fordelivery to a substrate, or for other use. A control system 4608 caninclude control circuits, processors such as microprocessors or otherprogrammable logic devices, memory such as RAM or ROM that storesprocessor-executable instructions for control of the beam perturbationdevice 4602 including, for example, one or more calibration tablescontaining beam perturbations as functions of beam perturbation devicedrive level. In some cases, the beam perturbation device 4602 caninclude one or more actuators or motors such as linear or steppermotors, piezoelectric stages, piezoelectric actuators, piezobendingmotors, bi-metallic strips (with thermal control), rotary motors, orvoice coil motors. Alternatively, the control system can include adigital to analog convertor (DAC) for setting drive levels to the beamperturbation device. For example, IPC-based beam perturbation devicesare responsive to applied voltages that can be provided by a DAC. A userinterface (UI) 4612 is typically provided that can include one or morecomputer input or pointing devices such as a mouse, trackpad, keyboard,or touchscreen for setting, adjusting, and recording and storing beamperturbation values. In some cases, control is via remote networkconnection and the control system 4608 includes a wired or wirelessnetwork interface. The UI 4612 can also include switches,potentiometers, and other devices for use in controlling the beamperturbation device 4602. In some examples, the beam perturbation device4602 includes a control system.

In some examples, a sensor 4610 is situated to determine beamperturbation or a condition of the beam perturbation device. The sensor4610 is coupled to the control system 4608 to correct errors and driftsin beam perturbations, and/or to verify that the beam perturbationdevice is operating as intended. For example, VBC apparatus that includean ionic polymer layer can be provided with one or more additionalelectrodes that are coupled to an amplifier or other circuit to producea signal indicative of layer deformation. This signal can be used tostabilize ionic polymer deformation. In other VBC apparatus, position,rotation, distance or other sensors can be included so thatperturbations produced by a perturbation device can be detected andcontrolled to maintain a selected perturbation.

FIG. 47A illustrates a VBC apparatus 4700 in which a fiber 4702 issecured to or guided by supports 4704, 4706. A fiber deflection member4708 (shown for purposes of illustration as having a circularcross-section) is situated to deflect an end portion 4703 of the fiber4702. The end portion 4703 can include a splice region 4704 in which afirst fiber and a second fiber are spliced. The fiber deflection member4708 is situated to push against the fiber 4702 to increase fiberdeflection and pull the fiber to decrease fiber deflection, but can besituated to push to decrease deflection and pull to increase deflection.

In another example shown in FIG. 47B, a VBC apparatus 4720 includes afiber 4722 that is in contact with, secured to, or otherwise restrainedby a support 4724. A fiber deflection member 4728 is situated to deflectthe fiber 4722 at a location at, near, or in a splice region 4730 inwhich a first fiber portion and a second fiber portion are splicedtogether. The fiber deflection members 4708, 4728 can have variousshapes and sizes and can be coupled to piezoelectric devices, linearmotors, or other actuators that provide displacement.

In another example shown in FIG. 47C, a VBC apparatus 4750 includes afiber 4752 that is in contact with, secured to, or otherwise restrainedby supports 4754, 4756. A fiber deflection member 4758 is situated todeflect the fiber 4752 at a location at, near, or in a splice region4760 in which a first fiber portion and a second fiber portion arespliced together.

The VBC apparatus 4700, 4720, 4750 do not include a fiber bendingsurface. Such a surface is convenient is some embodiments as shownabove, but is not required. In the examples of FIGS. 47A-47C, fiberdeflections are used. The fiber deflection members 4708, 4728, 4758 canhave various shapes and sizes and can be coupled to piezoelectricdevices, linear motors, or other actuators to provide displacements.

Having described and illustrated the principles of the disclosedtechnology with reference to the illustrated embodiments, it will berecognized that the illustrated embodiments can be modified inarrangement and detail without departing from such principles. Theparticular arrangements above are provided for convenient illustration,and other arrangements can be used.

We claim:
 1. An apparatus, comprising: a first fiber situated to receivean input optical beam, the first fiber having a first refractive indexprofile; a fiber shaping surface situated so that a section of at leastthe first fiber is urged to conform to the fiber shaping surface; a bendcontroller situated to select a length of the section of the first fiberurged to conform to the fiber shaping surface or to select a curvatureof the fiber shaping surface to perturb the input optical beam andproduce a modified optical beam; and a second fiber coupled to the firstfiber and situated to receive the modified optical beam, the secondfiber having a second refractive index profile selected to maintain atleast one beam characteristic of the modified optical beam.
 2. Theapparatus of claim 1, wherein the fiber shaping surface is a flexiblesurface.
 3. The apparatus of claim 2, wherein the fiber shaping surfaceis a major surface of a flexible plate.
 4. The apparatus of claim 3,wherein the flexible plate includes an ionic-polymer composite.
 5. Theapparatus of claim 4, wherein the flexible plate includes a first majorsurface and a second major surface, and further comprising a firstelectrode and a second electrode situated so that at least a portion ofthe ionic polymer is situated between the first electrode and the secondelectrode.
 6. The apparatus of claim 5, wherein the first electrode andthe second electrode are conductive layers that substantially cover thefirst major surface and the second major surface.
 7. The apparatus ofclaim 6, wherein the bend controller is an electrical voltage source. 8.The apparatus of claim 7, further comprising: a second set of electrodessituated about the ionic polymer; and a sensor coupled to the second setof electrodes to detect deformation of the flexible plate, wherein thebend controller is coupled to the sensor and establishes a voltageapplied to the ionic polymer based on a voltage detected by the sensor.9. The apparatus of claim 2, wherein the first fiber is situated toextend along a direction of the curvature of the fiber shaping surface.10. The apparatus of claim 2, wherein the first fiber comprises one ormore elongated loops and the section of the fiber conforming to thefiber shaping surface includes one or more portions of the loopssituated to extend in the direction of the curvature of the fibershaping surface.
 11. The apparatus of claim 2, further comprising adisplacement member coupled to the flexible plate to vary the curvatureof the fiber shaping surface.
 12. The apparatus of claim 11, wherein thedisplacement member is coupled to push against the flexible plate. 13.The apparatus of claim 11, further comprising a piezo-electric actuatorcoupled to the displacement member, wherein the displacement member iscoupled to pull the flexible plate.
 14. The apparatus of claim 1,wherein the fiber shaping surface comprises a plurality of fiber shapingsurfaces, wherein at least two of the plurality of fiber shapingsurfaces have different surface curvatures, and each of the plurality offiber shaping surfaces is situated so that sections of at least thefirst fiber are urged to conform to at least two respective fibershaping surfaces, and the bend controller is situated to select a lengthof the section of at least the first fiber to be urged to conform to acorresponding fiber shaping surface of the plurality of fiber shapingsurfaces.
 15. The apparatus of claim 11, wherein the flexible plate issecured at respective ends along a direction of the curvature of thefiber shaping surface.
 16. The apparatus of claim 1, wherein the fibershaping surface has a fixed curvature.
 17. The apparatus of claim 1,wherein the fiber shaping surface is a surface of a ring or a surface ofa section of a ring.
 18. The apparatus of claim 1, wherein the fibershaping surface is an outer surface of a cylinder.
 19. The apparatus ofclaim 18, the cylinder is a right circular cylinder.
 20. The apparatusof claim 16, wherein the bend controller is situated to vary the lengthof the section of the first fiber that conforms to the fiber shapingsurface.
 21. The apparatus of claim 1, further comprising a guideslidably secured with respect to the flexible surface and situated toengage the fiber so that the length of the section of the first fiberthat is urged to conform to the fiber shaping surface is variable inresponse to movement of the guide along the fiber shaping surface. 22.The apparatus of claim 20, wherein the guide includes a groove thatengages the first fiber.
 23. The apparatus of claim 21, wherein theguide is slidable so that the length of the section of the fiber thatconforms to the fiber shaping surface is greater than a circumferencedefined by the fiber shaping surface.
 24. The apparatus of claim 20,further comprising a connecting member rotatably secured at an axis ofrotation and secured to the guide so that rotation of the guide aboutthe axis urges the guide along the fiber shaping surface.
 25. Theapparatus of claim 24, wherein the fiber shaping surface has a compoundcurvature that includes a plurality of circular curvatures, and the axisof rotation corresponds to a center of curvature of one of the pluralityof the circular curvatures.
 26. The apparatus of claim 1, wherein thefiber shaping surface is defined by a portion of a mandrel surface andthe bend controller comprises a jaw situated to urge the first length offiber toward the portion of the mandrel surface.
 27. The apparatus ofclaim 26, wherein the first fiber forms at least a portion of a loopsituated about the mandrel.
 28. The apparatus of claim 27, wherein thebend controller includes a stage situated to urge the mandrel towardsthe first length of fiber.
 29. The apparatus of claim 28, wherein thefirst fiber and the second fiber form at least the portion of the loop,further comprising a splice that couples the first fiber and the secondfiber, wherein the jaw is situated to urge the first length of fiber, aportion of the second fiber, and the splice toward the portion of themandrel surface.
 30. The apparatus of claim 29, wherein the jawcomprises a first jaw and a second jaw oppositely situated with respectto a displacement axis of the stage, the first jaw and the second jawcoupled to a first elastic member and a second elastic member eachsituated to urge a respective jaw surface toward the mandrel surface.31. The apparatus of claim 30, wherein the bend controller is configuredto urge the mandrel toward the first jaw surface and the second jawsurface so as to select the section of the first fiber that is urged toconform to the fiber shaping surface, a section of the second fiber thatis urged to conform to the fiber shaping surface, and a curvature of atleast a portion of the loop that does not contact either the fiberbending surface, the first, jaw, or the second jaw.
 32. An apparatus,comprising: a first fiber situated to receive an input optical beam, thefirst fiber having a first refractive index profile; a bend controllersituated to select a bend of at least a section of the first fiber toperturb the input optical beam and produce a modified optical beam; anda second fiber coupled to the first fiber and situated to receive themodified optical beam, the second fiber having a second refractive indexprofile selected to maintain at least one beam characteristic of themodified optical beam.
 33. The apparatus of claim 32, wherein thesection of the first fiber extends from a fiber support.
 34. Theapparatus of claim 32, wherein the section of the first fiber issituated between a first fiber support and a second fiber support.